The present invention relates to polymers containing fluorine groups and also to coating compositions prepared from these polymers.
It is desirable in a variety of applications such as building products to prepare coating compositions from film forming binders based on fluoropolymers because these materials tend to be very durable. Not only do coating compositions based on fluorocarbon resins provide a tough finish, but they also provide a finish that will not craze or chalk upon extended outdoor exposure. As a result, such coating compositions are highly recommended for use in environments with agressive climatic conditions. As was mentioned above, these coatings are especially suited for the building products industry, particularly in the preparation of steel building panels.
Especially suited for these applications where durability is important are the fluoroolefin polymers wherein the fluorine content of the polymer is high. Such polymers can be derived from the common fluoroolefin monomers such as vinyl fluoride, vinylidene fluoride, tetrafluoroethylene, perfluorohexylethylene and chlorotrifluoroethylene The preparation of fluoroolefin polymers, however, is not without difficulty. While the aforesaid fluorine containing vinyl monomers can be polymerized with nonfluorine-containing vinyl monomers, the variety of polymeric structures is limited due to the unusual reactivity parameters of fluorine containing vinyl monomers. In addition to the difficulties attendant to the preparation, once the polymerization is complete, the resultant polymers are difficult to formulate into high solids compositions because of their poor solubility and other physical properties such as molecular weight, functionality, etc. Even when the preparation can be done readily other problems arise. For example, it is known to polymerize fluoroolefin monomers with vinyl esters or vinyl acetate in order to improve solubility and introduce curable functionality into the fluoroolefin polymer. This technique, however, often results in a polymer in which the fluorine units are distributed in an alternating fashion, therefore a polymer with a high fluorine content is not readily obtained.
Other difficulties also arise as a result of the particular method of preparation. For example, in procedures which utilize chain transfer agents, often the chain transfer agent is ineffective. When it is effective other factors must be dealt with. For example, the resultant polymer will contain some proportion of linkages other than carbon carbon bonds which are introduced as a result of the chain transfer agent, e.g., carbon sulfur bonds. These are generally undesirable.
There is a need, therefore, for fluorine containing vinyl polymers which contain a high fluorine content, are relatively easy to prepare from inexpensive starting materials which can be readily formulated into thermosetting coating compositions.